Polyarylene sulfides (hereinafter may be abbreviated as PAS) as typified by polyphenylene sulfides (hereinafter may be abbreviated as PPS) are resins having favorable properties as engineering plastics such as excellent heat resistance, barrier property, chemical resistance, electric insulation, moist heat resistance and flame resistance. The polyarylene sulfides are moldable by injection molding or extrusion molding to various molded components, films and sheets and fibers and are used in a wide range of fields needing the heat resistance and the chemical resistance, such as various electric and electronic components, mechanical components and automobile components.
A specific manufacturing method of this polyarylene sulfide has been proposed to use the reaction of an alkali metal sulfide such as sodium sulfide with a polyhalogenated aromatic compound such as p-dichlorobenzene in an organic amide solvent such as N-methyl-2-pyrrolidone. That method is widely used as the industrial manufacturing method of polyarylene sulfide. That manufacturing method, however, has some problems, i.e., need for the reaction under the high temperature, high pressure and strongly alkaline conditions, need for an expensive high boiling-point polar solvent such as N-methylpyrrolidone, energy-intensive with high cost for recovery of the solvent and need for enormous processing cost.
Additionally, the polyarylene sulfide manufactured by that method has a low molecular weight and a very wide distribution of molecular weight as a whole and is not desirable in application of the molding process. More specifically, the polyarylene sulfide is a polymer having a very high polydispersity of 5.0 to 20 expressed by (weight average molecular weight Mw/number average molecular weight Mn). Accordingly, application of the polyarylene sulfide obtained by the above method to the molding process causes some problems, for example, insufficient mechanical properties, a high gas generation amount under heating and a large amount of eluted component during exposure to a solvent. In manufacturing the polyarylene sulfide by the above manufacturing method, a process of increasing the molecular weight by, for example, thermal oxidative cross-linking in the air is needed. This complicates the process and lowers the productivity (for example, JP S45-3368B). The process of increasing the molecular weight causes a partial component of the polyarylene sulfide having the wide distribution of molecular weight to have an excessively high molecular weight. In that case, the high molecular weight component leads to deterioration of the flowability and the moldability, whereas the low molecular weight component leads to deterioration of, for example, the mechanical strength and the chemical resistance.
A manufacturing method of polyarylene sulfide by heating a cyclic polyarylene sulfide has been disclosed as another manufacturing method of polyarylene sulfide. That method is expected to obtain a polyarylene sulfide having a high molecular weight, a narrow distribution of molecular weight and a little weight loss under heating (for example, WO 2007/034800 and Polymer, Vol. 37, No. 14, 1996 (pages 3111 to 3116)). The polyarylene sulfide manufactured by that method is, however, expected to have no terminal structure or even if any, only a very small amount of terminal structure obtained by impurities or side reactions in the course of polymerization. Accordingly, that method gives a polymer having uncertainty in the presence or the absence of the terminal structure and the amount of the terminal structure. The polyarylene sulfide without the terminal structure or with only a very small amount of the terminal structure is expected to have such problems as poor compatibility with a filling material such as filler, another thermoplastic resin and a thermosetting resin and insufficient mechanical properties.
As the above manufacturing method of the polyarylene sulfide by heating the cyclic polyarylene sulfide, a manufacturing method of a polyarylene sulfide resin composition having a low weight reduction ratio ΔWr of not higher than 0.18% under heating has been disclosed, which mixes an olefin copolymer containing an epoxy group with an olefin copolymer without an epoxy group. The polyarylene sulfide obtained by that method, however, has the low gas generation amount and the improved molding processability but provides only insufficient compatibility between PAS resin and the epoxy group-containing olefin resin and accordingly does not give the practically satisfying level of toughness (for example, JP 2008-222889A).
Another manufacturing method of a similar polyarylene sulfide resin composition having the low weight reduction ratio ΔWr of not higher than 0.18% under heating has been disclosed, which mixes a polyphenylene sulfide with fibrous and non-fibrous filling materials. The resin composition obtained by that method, however, has the low gas generation amount but insufficiently improved filler adhesiveness and does not give the practically satisfying level of mechanical properties (for example, JP 2008-231141 A).
A number of methods of introducing a functional group to polyarylene sulfide including a method that does not use the above cyclic polyarylene sulfide have been known as the method of providing polyarylene sulfide with the reactivity. One exemplary method melt kneads a polyarylene sulfide obtained by a conventional reaction with a compound having a functional group such as an alkali metal salt of an organic compound or maleic anhydride (for example, JP H11-286548A and JP H02-283763A).
Another exemplary method introduces a functional group to the polymer main chain by copolymerization of a functional group-containing polyhalogenated compound in the course of polymerization of the polyarylene sulfide (for example, JP H07-102064A).
Those methods, however, have the problem of complicated operations to introduce a certain amount of the functional group to achieve the sufficient effects. The methods described in the above JP H11-286548A, JP H02-283763A and JP H07-102064A use the conventional PAS and accordingly do not solve the problems of the conventional PAS, e.g., the high gas generation amount and the wide distribution of molecular weight.
Another disclosed method of manufacturing polyarylene sulfide polymerizes a cyclic arylene sulfide oligomer by ring-opening polymerization under heating in the presence of an ionic ring-opening polymerization catalyst. That method is expected to obtain a polyarylene sulfide containing a functional group and having a narrow distribution of molecular weight. That method, however, uses an alkali metal sulfur compound, such as sodium salt of thiophenol, as the ring-opening polymerization catalyst for synthesis of polyarylene sulfide and accordingly has a problem that a significant amount of the alkali metal remains in the resulting polyarylene sulfide. More specifically, increasing the amount of the ring-opening polymerization catalyst used to increase the amount of the functional group for the purpose of providing the reactivity causes problems, for example, increasing the amount of the alkali metal remaining in the polyarylene sulfide and decreasing the molecular weight of the resulting polyarylene sulfide. That reduces the reliability in applications that need the electrical insulating properties and limits expansion to applications that need the sufficient mechanical properties. Additionally, the above method of ring-opening polymerization also achieves only an insufficient decrease in gas generation amount (for example, JP H05-301962A, JP H05-163349A and JP H05-105757A).
It could therefore be helpful to provide an industrially useful polyarylene sulfide resin composition that includes a reactive functional group and has low gas generation and a narrow distribution of molecular weight.